Self-tapping implants are designed to be screwed into bone. During a typical surgical implantation procedure, the implantation site is exposed; and a hole is drilled into the bone. The end of the self-tapping implant is then positioned into the hole and the implant is screwed downwardly to the desired position. As the implant rotates, it simultaneously taps threads and screws into these threads.
A typical self-tapping implant has a first end for tapping threads in the bone, a second end for connecting to a prosthesis, and a threaded middle section for engaging the threads tapped in the bone. The tapping end of the implant usually consists of several grooves or flutes that extend upwardly on the sidewall of the implant along the longitudinal axis of the implant. Each flute includes a cutting edge that scrapes off bone as the implant is rotated into the hole. The cutting edges form threads along the bone for engaging the threaded section of the implant.
Present self-tapping implants offer many advantages over non-tapping implants. First, a separate bone tapping tool is not required since the implant itself taps the bone. Second, the overall time to perform the surgical implantation procedure is reduced since the bone does not first have to be separately tapped before the implant is inserted into the hole. As another advantage, self-tapping implants generally have a more intimate contact with the surrounding bone than non-tapping implants.
In spite of the foregoing advantages, present self-tapping implants also possess numerous disadvantages. For example, irregularities or defects may exist on the bone around the entrance of the hole at the implantation site. These irregularities may occur naturally or as a result of the surgical procedure, and these irregularities further may inhibit bone integration with the implant. Prior self-tapping implant designs do not remedy these irregularites.
As another disadvantage, bone chips tend to accumulate at the cutting edge while the implant is being tapped into the bone. These bone chips decrease the effectiveness of the cutting edge and further increase the insertion torque required to insert the implant. The tapping end of the implant should have a geometry to cut bone chips and then direct these chips away from the cutting edge.
As yet another disadvantage, some prior self-tapping implants push bone chips downwardly or away from the threads on the implant. If these bone chips were directed to tightly pack around the threads, then the implant would be more stable in the bone.